Being one tissue in the mammalian body that regenerates in postfetal life, bone is a promising tissue for research on morphogenetic macromolecules, heretofore undiscovered derivatives of phenotypic cell surface molecular assemblies. The proposed research deals with the following hypothetical constituents: the bone morphogenetic protein (BMP), and insoluble polypeptide firmly attached to collagens of bone, dentin, and other calcified tissues; neutral proteinase (BMPase), geographically in close association with, but separable from BMP; BMPase-inhibitor, a soluble non-collagenous protein surrounding BMPase; BMP-inhibitor, a high molecular weight soluble protein in juxta position to BMP. The investigative procedures are designed to separate and purify the constituents of the bone morphogenetic system either by digestion of bone matrix with collagenase, or by chemical extraction without enzymic degradation or by the combination of the two. The methods include: filtration of digest or extract on gel columns at different levels of pH; chromatography on ion-exchangers; paper or column electrophoresis under acidic conditions. The morphogenetic constituents are demonstratable and bioassayed in: (a) residues of matrix inplanted in muscle in rats (b) isolated substances added to chemically-defined culture media in vitro in systems consisting of mesenchymal cell outgrowths of muscle into substrata prepared from denatured bone matrix; (c) isolated proteins on a millipore membrane-substratum for outgrowths of mesenchymal cells from chick chorio-allantoic membrane.